The combustion events in an IC engine can be analyzed on a real-time basis for purposes of diagnosing and/or controlling the engine operation. Several useful combustion parameters, including the indicated mean effective pressure (IMEP), the pumping mean effective pressure (PMEP) and the net heat release energy (Qnet), can be calculated based on engine cylinder pressure measurements and corresponding cylinder volume data. These combustion parameters can be used to detect combustion irregularities in a given cylinder and to detect cylinder-to-cylinder imbalances.
The pressure-based combustion parameters for a given cylinder are ordinarily determined by periodically measuring the cylinder pressure with a suitably placed pressure sensor, calculating cylinder volume data for each pressure measurement based on crankshaft position (also referred to herein as crank angle), and calculating the combustion parameters based on the measured pressures and the calculated cylinder volume data. However, calculating the combustion parameters with sufficient resolution requires an enormous computational effort, and it can be difficult to accurately associate individual pressure measurements with corresponding cylinder volume data. What is needed, therefore, is a method of more efficiently determining pressure-based engine combustion parameters with an on-board engine controller.